Multiple wavelength led array illuminator for fluorescence microscopy

ABSTRACT

One embodiment provides light along an optical axis. It comprises a substrate and at least one array of multiple LED chips without individual packaging supported by the substrate. The LED chips emit light within different wavelength ranges and are distributed laterally with respect to the axis over an area, the LED chips having light emitting surfaces for emitting light in directions transverse to the area. An optical element adjacent to the light emitting surfaces of the LED chips in the at least one array collects and directs light emitted by the LED chips of the at least one array along the axis towards a target. Another embodiment is directed to a method for providing multiple wavelength light for fluorescent microscopy using the above system. Electric current is supplied to the multiple LED chips, causing them to emit light of multiple wavelengths. The currents supplied to the multiple LED chips are controlled so as to control the exposure of fluorescent dyes with different excitation wavelengths wherein the light emitted by the multiple LED chips include wavelength components at such different excitation wavelengths without having to move the multiple LED chips.

BACKGROUND

The present invention relates generally to illumination apparatuses usedfor purposes such as fluorescence microscopy, and specifically to anillumination apparatus comprising a multiple wavelength light emittingdiode (LED) array and its accompanying optical elements.

Fluorescence microscopy is popularly used in numerous bio/medicalapplications since it enables users to label and observe specificstructures or molecules. Briefly, fluorescence is a chemical processwhere when light of a specific wavelength is shined upon a fluorescentmolecule, electrons are excited to a high energy state in a processknown as excitation. These electrons remain briefly in this high energystate, for roughly a nanosecond, before dropping back to a low energystate and emitting light of a lower wavelength. This process is referredto as fluorescent emission, or alternatively as fluorescence.

In a typical fluorescence microscopy application, one or more types offluorescent materials or molecules (sometimes referred to as fluorescentdyes) are used, along with an illuminator apparatus that provides theexciting wavelength, or wavelengths. Different fluorescent molecules canbe selected to have visually different emission spectra. Since differentfluorescent molecules typically have different excitation wavelengths,they can be selectively excited so long as the bandwidth of theexcitation light for one fluorescent molecule does not overlap theexcitation wavelengths of other fluorescent molecules that are beingused in the same experiment. Therefore the excitation light shouldideally have a narrow bandwidth and have its peak output at theexcitation wavelength of the molecule in question. Furthermore,fluorescence is a probabilistic event with low signal levels so anintense light is typically used to increase the chances of the processoccurring. Most fluorescence microscopy applications also benefit fromhaving a uniformly intense illuminated field of view or area, ideallysuch that the size and shape of the illuminated area can be modified.Simultaneously achieving all these criteria has been difficult but isnecessary for current and future applications that require increasinglevels of illumination control and consistency.

Traditional prior art fluorescence microscopy illuminators have reliedon metal halide arc lamp bulbs such as Xenon or Mercury bulbs, as lightsources. The broad wavelength spectrum produced by these lamps whencombined with specific color or band pass filters allows for theselection of different illumination wavelengths. This wavelengthselection and light shaping process, however, is highly energyinefficient since in selecting only a relatively small portion ofwavelength spectrum produced by the Xenon or Mercury bulb, the vastmajority of the light outputted from the lamp is unused. Thesewavelength selection or band pass filters are costly, especially whenplaced on a mechanical rotating wheel in typical multiple-wavelengthapplications.

In this type of implementation using metal halide arc lamp bulbs, thespeed with which different wavelengths can be selected is limited by themechanical motion of moving various filters into place. In addition tothe sluggishness and unreliability of filter wheels, as well as energycoupling inefficiency, metal halide arc lamps are also hampered by thelimited lifetime of the bulb, typically ˜2000 hours. The intensity ofthe light output declines with bulb use and once exhausted, the user hasto undergo a complicated and expensive process of replacing the bulb andsubsequently realigning the optics without any guarantee that theilluminator will perform as before. These disadvantages make acquiringconsistent results difficult and inconvenient for users who must dealwith the variable output of the bulbs, and who must either be trained inoptical alignment or call upon professionals when a bulb needs to bereplaced.

In recent years, several prior art multiple wavelength illuminators havebeen developed using different colored LEDs as light sources, thatovercome numerous limitations of metal halide arc lamps. Not only dothey last longer, with the lifetime of an LED chip being typically ratedat well over 10,000 hours, but in addition the power output variesnegligibly over that period. Furthermore, the bandwidth of the spectraloutput of an LED chip is typically narrow (<30 nm) which can eliminatethe need for additional band pass filters and is ideal for fluorescenceapplications. The intensity of the output light can be quickly andaccurately controlled electronically by varying the current through theLED chip(s), whereas in metal halide illuminators, the output intensityof the bulb is constant and apertures or neutral density filters areused to attenuate the light entering the microscopy.

Prior art LED illuminators for fluorescence microscopy have thus farused up to 5 separate LED modules, each containing one up to a fewchips, for each wavelength. Since the LED chips in these modules havetheir own individual packaging, the modules are large so that lightbeams emitted from the modules will need to be combined using opticalelements. Although such prior art LED illuminators allow the user theflexibility to swap out modules for new modules with differentwavelengths, the additional elements such as lenses, mirrors and heatsinks required for each separate color add complexity, bulk and cost.Furthermore, the long optical paths required to combine the beams frommultiple LED chips or modules that are spatially separated, make itdifficult to collect and shape already highly divergent light comingfrom the LED chips. These practical issues have limited the applicationof such illuminators in fluorescence microscopy, which in generalrequires light that is both intense and spatially uniform.

SUMMARY OF THE INVENTION

One embodiment of the invention is directed to a multiple wavelength LEDarray illuminator for providing light along an optical axis, whichcomprises a substrate and at least one array of multiple LED chipswithout individual packaging supported by the substrate, wherein the LEDchips emit light within different wavelength ranges and are distributedlaterally with respect to the axis over an area, the LED chips havinglight emitting surfaces for emitting light in directions transverse tothe area. The illuminator includes an optical element adjacent to thelight emitting surfaces of the LED chips in the at least one array thatcollects and directs light emitted by the LED chips of the at least onearray along the axis towards a target. Additional optical elements,including a light collecting lens of preferably large numericalaperture, a light scrambler or homogenizer, an aperture, and a focusingor collimating lens of preferably large aperture and diameter, serve tocreate a collimated (or nearly collimated) beam of preferably highspatial uniformity, that is directed into the target microscope.

Another embodiment is directed to a method for providing multiplewavelength light for fluorescent microscopy. A LED array illuminator isprovided that includes a substrate, at least one array of multiple LEDchips without individual packaging supported by the substrate, whereinthe LED chips emit light within different wavelength ranges. Electriccurrent is supplied to the multiple LED chips, causing them to emitlight of multiple wavelengths.

The currents supplied to the multiple LED chips are controlled so as tocontrol the exposure of fluorescent dyes with different excitationwavelengths wherein the light emitted by the multiple LED chips includeswavelength components at such different excitation wavelengths withouthaving to move the multiple LED chips.

All patents, patent applications, articles, books, specifications, otherpublications, documents and things referenced herein are herebyincorporated herein by this reference in their entirety for allpurposes. To the extent of any inconsistency or conflict in thedefinition or use of a term between any of the incorporatedpublications, documents or things and the text of the present document,the definition or use of the term in the present document shall prevail.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a representation of the prior art of a typical multiplewavelength fluorescence microscopy illuminator using a Xenon or Mercurylamp and color filter wheel to select the wavelength.

FIG. 2 is a representation of the prior art in multiple wavelengthfluorescence microscopy LED illuminators using separate LED modules foreach different wavelength.

FIG. 3 is a block diagram representation of the present invention andillustrates the different components and their function in theapparatus.

FIG. 4A is a representation of one embodiment of the present inventionusing a diffuser plate as a light scrambler/randomizer. FIG. 4B shows across-section view of the optical elements of one practicalimplementation of one embodiment of the present invention.

FIGS. 5A and 5B show polar and rectangular coordinate plots of the lightoutput of the LED array used in one embodiment of the present invention,including the half-ball lens that sits over the LED array.

FIG. 5C provides plots of the light uniformity of the beam that exitsthe optical elements of one embodiment of the present invention, showingthe relative effects of different aperture dimensions and differentdiffusers.

FIG. 6A is a perspective view of one embodiment of the LED arrayassembly from the present invention where lateral translation of thearray enables different regions of the array to be aligned with theoptical axis (shown in isometric view).

FIG. 6B is another perspective view of one embodiment of the LED arrayassembly in which several LED arrays each having its own lens arearranged in close proximity and lateral translation enables differentarrays to be aligned with the optical axis (shown in isometric view).

FIG. 7A is a schematic view of one embodiment where the light comingfrom the embodiment in FIG. 4 is sent into a zoom lens system to expandor contract the beam width.

FIG. 7B is a schematic view of another embodiment where a mirror isplaced between the embodiment in FIG. 4 and zoom lens system shown inFIG. 7A to redirect the light path.

FIG. 8 is a schematic view of yet another embodiment of the presentinvention, using a light mixing tube as a light scrambler/randomizer andthe variable distance between the collector lens and tube entrance as ameans to change aperture size.

FIG. 9A is a representation of one embodiment of the densely packedmultiple wavelength LED array used in the present invention, with 24 LEDchips without individual packaging.

FIG. 9B shows a cross section of the densely packed multiple wavelengthLED array from FIG. 9A.

FIG. 9C is a representation of one configuration of LED array using 3LED chips per channel (8 channels total).

FIG. 10 is a representation of one embodiment that uses a narrow bandpass filter wheel after the representation from FIG. 4 to further narrowthe bandwidth of each color.

Identical components in this application are labeled by the samenumerals.

DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

A compact multiple wavelength illuminating apparatus is disclosedherein, comprising one or more LED array with accompanying opticalelements that outputs intense, spectrally narrow light uniformly over afield of view. The LED array contains multiple strings, each stringcomprising several LED chips of the same wavelength, where thewavelength of each string is preferably different from wavelengths ofthe other strings, with each string controlled electronically as aseparate channel. Alternatively, each string may comprise LED chips thatemit different wavelengths, where the group of wavelengths emitted byeach string is different from the groups of wavelengths emitted by theother strings, and where there can be overlap between the groups ofwavelengths emitted by the different strings.

Several major advantages result from the use of an LED array thatcontains LED chips of multiple wavelengths, organized into separatelycontrolled strings. Multiple exciting wavelengths suppliedsimultaneously enable the selective excitation of multiple fluorescentmolecules or dyes, within the same experiment. It may also avoid theneed to change out the light sources when multiple researchers are usingthe same equipment for their experiments, but are using differentfluorescent molecules or dyes. The multiple channels allow for eachstring of LEDs and hence output color and power to be rapidly switchedon/off and varied in intensity, respectively.

The optical elements immediately succeeding the LED array serve tocollect and reshape the output light to enhance both light couplingefficiency and uniformity. A lens attached to the surface of the LEDarray enhances light extraction, and is followed by another lens oflarge numerical aperture, that is used to collect the light and send itthrough a light scrambler which acts to spatially homogenize the beam.An aperture, used to cut off undesired light on the perimeter of thebeam, is followed by a focusing or collimating lens of large apertureand diameter, after which the light either enters a microscope oradditional optical elements such as fiber couplers or beam expanders foradditional light shaping. The apparatus allows for minor adjustments tobe made in the positioning of the optical elements along the opticalaxis, to compensate for optical differences between different brands ofmicroscopes. Furthermore, translational lateral movement of the arrayenables different regions of the LED chip array to be aligned along theoptical axis to enhance optical performance. Interchangeable mountingadapters allow the apparatus to be used with multiple brands ofmicroscopes. The resulting illuminating beam, with high brightness and ahigh degree of uniformity, ensures that the fluorescence of sampleswithin the beam is consistent and repeatable.

As fluorescence microscopy becomes increasingly popular in bio/medicalapplications the demand for powerful, reliable, and affordableillumination sources has increased as well. Fluorescence microscopy hasevolved as a tool not only for viewing specific structures, but forquantitatively measuring their distribution and dynamics as well. Thesequantitative measurements benefit from illumination sources that arestable over long periods of time and will last at least the lifetime ofthe experiment or project. To increase time resolution, faster exposuretimes are being used which typically requires a stronger excitationsignal and hence intense illumination. Furthermore, to simplifybackground calibrations, the illumination area, which can be larger thanthe microscope's field of view, should be uniform in intensity.Simultaneously achieving all the above features of an ideal fluorescenceilluminator has been thus far either exceedingly difficult and/orexpensive. The present invention overcomes several of the disadvantagesof prior art multiple wavelength fluorescence microscopy illuminatorsand satisfies the needs for many fluorescence applications.

Although multiple wavelength illuminators have been realized usingtraditional metal halide arc lamps with selective filters, thistechnology has been limited mainly by the inherent widespread spectraldistribution of the lamps. Metal halide fluorescent microscopyilluminators work by filtering out unwanted wavelengths, but because thepower of the light source is distributed over a wide range ofwavelengths, only a small fraction of it goes into the desired filteredwavelength. Thus metal halide illuminators are often considered to beunderpowered. The need for mechanical filter wheels also makes switchingcolors relatively slow, typically a fraction of a second, when comparedto the sub-microsecond time scale of turning LEDs on and off.

A typical carousel filter wheel is shown in FIG. 1, as item 102, withits direction of rotation indicated by item 103. Since the lamp filamentin metal halide arc lamp bulb 100 which emits light is an extended lightsource, significant optical treatment must be done to make theillumination area uniform. This typically involves either usingdispersive diffusers (FIG. 1, item 104) or field stops and apertures(not shown) for Koehler illumination, for instance, both of which cuteven more power. Lastly metal halide arc lamps are hampered by the shortlifetime of the bulbs, over which lifetime the intensity continuallydecays. Most lamps require a warm-up period of around 30 minutes whichcan be inconvenient for users with time sensitive samples. Rated to lastroughly a few hundred hours, bulbs must often be replaced several timesa year which is not only inconvenient and expensive, but difficult andoften requires the hiring of professionals. Alignment typically requiresadjusting the many degrees of freedom of a reflector surrounding thebulb (FIG. 1, item 101, adjustment along arrows 107, and 108) which isnot necessarily a tedious process, but often requires training and ishence inaccessible to many users unfamiliar with optics.

Prior art multiple wavelength LED illuminators have overcome some of thelimitations of metal halide ones but have been complicated, requiringmany optical elements, and hence costly to manufacture. LEDs emit lightwith narrow bandwidth (typically ˜10-30 nm for a specific LED chip),ideal for most fluorescence applications. Unlike metal halide bulbs, LEDchips have lifetimes rated at well over 10,000 hours and do not requirea warm up period before reaching full output. The ability to havemultiple wavelengths is achieved by using LED chips that emit differentcolors. Each LED chip resembles a point source more than metal halidebulbs do and therefore it is usually easier to homogenize theillumination intensity distribution.

In the prior art embodiment shown in FIG. 2, each wavelength comes fromseparate LED “modules” (FIG. 2, items 201-204). Since prior art LEDseach has its own packaging, the LED modules are relatively large, sothat each module will need to have its own set of collecting andcollimating optics (items 201A-204A), whose light paths are combinedusing dichroic mirrors (items 205-207). Having separate modules,however, requires long optical paths. In order to collect the maximumamount of light, this prior art embodiment requires large lenses withlarge numerical apertures that are both costly and bulky. The maximumnumber of LED wavelengths that can be equipped at any one time is alsolimited by the cost and complexity of the beam-combining optics.

The present invention of a multiple wavelength fluorescence illuminationapparatus uses a densely packed LED chip array, where the LED chips donot have individual packaging to allow dense packing of the chips in thearray, and is both compact and uses far fewer optical elements than theprior art LED illuminators which use modules. The LED chips in the arrayare preferably supported on a single substrate and the array has asingle package for housing all of the chips in the array, resulting in amodule with multiple LED chips. The dimensions of the light emittingarea of the LED array are less than 25 mm, and are typically in therange of 8-15 mm. The light emitting area of the LED array is preferablycircular in shape and has a diameter less than 25 mm and typically inthe range of 8-15 mm. The number of wavelengths provided within thearray depends on the specific design of the LED array, and on the needsand requirements of the users of the illuminator apparatus. A typicalembodiment of the present invention would include at least fourwavelengths of LEDs, and might include as many as 8, 10, or even 12wavelengths. Including more wavelengths within a single LED array givesthe users of the apparatus more choices of fluorescent molecules or dyesto use in their experiments. This may be important in environments wheremultiple users are sharing equipment. The multiple wavelengths, or asubset of them, may also be used simultaneously, in experiments thatrequire the use of multiple, selectively-excited fluorescent dyes.

A schematic block diagram illustrating the major components in theapparatus of one embodiment of the present invention is shown in FIG. 3,with the optical elements of one implementation of the embodiment shownin more detail in FIG. 4A. The light emitted from the LED chips withinthe LED array assembly has a Lambertian distribution. Since the index ofrefraction of the chips is high (3.4 for GaAs-based LED chips, and 2.3for GaN-based LED chips), a lens such as a half-ball lens (item 4A02) isattached to the top of the LED array (item 4A01) with a refractive indexmatching gel such as silicone filling the space between the LED chipsand the half-ball lens, to reduce total reflection at the LED surfacesand improve light extraction. The diverging light from the LED array isthen immediately collected by a condensing lens (item 4A03) of highnumerical aperture (small f-number). Afterwards, the light ishomogenized using a light scrambler/randomizer (item 4A04) and aperture(item 4A05) such that the intensity distribution is uniform over theilluminated area entering the microscope.

The light scrambler (item 4A04) can be any kind of material that evenlydistributes light, for instance by having randomly textured surfaces orimbedded diffractive particles. In one embodiment of the presentinvention, an engineered diffuser is used, that provides a non-Gaussian,circular “top-hat” beam pattern, with a flatter beam intensity profilethan would be obtained from a traditional diffuser. This form ofdiffuser aids in achieving a highly uniform beam pattern. Said “top-hat”diffusers are available from multiple vendors, and achieve their shapedbeam profile, with a high degree of beam uniformity, through the use ofan engineered surface, consisting of a large number of microlenses.These microlenses are fabricated with a known pattern to create thedesired overall beam shape, but the parameters of the individualmicrolenses are randomized in order to create a diffuse beam that isrelatively insensitive to the spatial characteristics of the input beam.These engineered diffusers are available in a variety of beam shapes,including beams with circular, square and line-shaped cross-sections,all with good uniformity. The type used in one embodiment of the presentinvention provides a beam with a circular cross-section.

A focusing lens/collimator of relatively large aperture and diameter(item 4A06) is placed at the end of the light path before entering thetarget microscope, represented in FIG. 4A by item 4A11. Though notdescribed in detail, other kinds of lenses that improve lightextraction, collection, and collimation are within the scope of thepresent invention. FIG. 4B provides a cross-section view of the opticalelements of one embodiment of the present invention in which aplano-convex lens (item 4B03) and diffuser plate (item 4B04) are used asthe light collector and scrambler, respectively. In the embodiment shownin FIGS. 4A and 4B, the positions of both the light collector lens(items 4A03 and 4B03) and the focusing lens/collimator (items 4A06 and4B06) can be adjusted slightly (along arrows 4A03′ and 4A06′) along theoptical axis, by means known to those in the art, such as by means ofsliding lens mounts or lens holders. Note that in the embodiment shownin FIG. 4B, the adjustment of the light collector lens (4B03) also movesthe diffuser plate (4B04) and aperture (4B05), which in this embodimentare fixed in relation to the light collector lens (4B03). Theadjustability of the lenses is used to optimize the optical performanceof the apparatus, to work with different brands of fluorescencemicroscopes. The adjustment may be performed using adjustment mechanisms4A08 and 4A09 in a known manner. Although separate adjustment mechanismsare shown in FIG. 4A, it is within the scope of the present invention tohave a single adjustment mechanism. Note that items 4B01 through 4B06 ofFIG. 4B correspond to the similarly numbered items 4A01 through 4A06 ofFIG. 4A. The focusing lens/collimator (4A06 and 4B06) forms andcollimates the beam towards a target (not shown) in fluorescencemicroscopy. In addition, FIG. 4B shows a representative mounting adaptor(4B07), used to mount the illuminating apparatus to the microscope (notshown). It also shows a heat spreader and heat sink (4B08) mounted tothe back side of the LED array (4B01).

FIGS. 5A and 5B provide polar and rectangular coordinate plots of thelight output of the LED array used in one embodiment of the presentinvention, including the effect on the light output of the half-balllens that is affixed to the surface of the LED array. As can be seen inthese figures, the LED array and half-ball lens provide a fairly widebeam, but with insufficient uniformity of light intensity across thebeam. In contrast, FIG. 5C shows several plots of the light intensityacross the beam that is emitted from the entire apparatus of oneembodiment of the present invention, where a “top-hat” type diffuser isused. The three plots of FIG. 5C represent differing combinations ofaperture diameter and the angle of the diffuser element. As expected theplot obtained with an aperture of 12 mm diameter shows a narrower beam,compared to the plots taken with an aperture of 15 mm. But in all cases,the beam is highly uniform, with sharply-defined beam boundaries.

The optics of the present invention are optimized to work with a pointsource, with light output that is aligned with the optical axis, whereasthe actual LED array, though densely packed, is more of anquasi-extended point source. If a fixed position of the LED array doesnot provide sufficient light uniformity for all of the differentwavelengths provided within the LED array, then it is possible toincorporate a movable mount (not shown) for the LED array, where themovement of the mount is caused by an adjustment mechanism 4A10, used ina known manner, such as x-axis and y-axis position adjustment screws,for translational motion along arrows 4A07. Using such a mount, thearray can be positioned or translated, and the LED chips on the arraycan be arranged, such that the LED array, or the illuminated portion ofthe LED array, behave similarly to a point source. For many applicationsthe different colors or wavelengths of LED chips within the array willall be located close enough to the optical axis (e.g. LED chips locatedless than about 10 or 15 mm from the optical axis) such that sufficientuniformity of the light output will be obtained, without movement ortranslation of the array, regardless of which color or wavelength isselected, and therefore regardless of which subset of LED chips withinthe array is illuminated.

However, where maximum uniformity of the light output is required, theposition of the LED array can be laterally moved or translated to betteralign different regions of the LED array with the optical elements ofthe illuminator and to improve optical performance, since the optics areoptimized for point sources along the optical axis. The translationaldegrees of freedom shown by FIG. 4A, motion along arrows 4A07 allowdifferent regions of the LED array to be aligned with the optical axis.These degrees of freedom are represented in more detail by items 6A01and 6A02 in FIG. 6A, which represents one embodiment of the LED chiparray, where the LED chips supported by a common substrate (e.g. printedcircuit board) are grouped into four subsets each emitting one of fourwavelengths (390 nm, 470 nm, 520 nm and 610 nm in this example). Forsome applications, preferably the wavelengths emitted by the LED chipsincludes one in the ultraviolet range. Other wavelengths may be used,depending on the requirements of the fluorescent dyes that are to beexcited. The array is arranged such that each wavelength of LED chipemitted from one of the four subsets is densely clustered in one of thefour different regions of the array where the subset of LED chips ineach of these regions can be aligned with the optical axis. FIG. 6Billustrates another embodiment in which the LED array apparatus containsseveral arrays side-by-side supported by a common substrate (e.g.printed circuit board), each array equipped with its own half-ball lens,and also uses translation (as represented by items 6B01 and 6B02) of theposition of the arrays, such that different regions and/or arrays arealigned with the optical axis. Each of the four arrays of LED chips mayemit light within a wavelength range that is different from those oflight emitted by at least one of the remaining three arrays.

While FIG. 6A illustrates an embodiment where each subset of LED chipsemits the same wavelength. It will be understood, however, that this isnot required. There may be applications where it is desirable for thelight supplied to the microscope have different wavelengths for excitingdifferent fluorescent dyes. For this purpose, it may be desirable forany one of the four subsets in FIG. 6A to contain LED chips that emitdifferent wavelength light, to supply light to the microscope havingdifferent wavelengths for exciting different fluorescent dyes in thesame experiment without having to move the LED chips at all.

Where certain combinations of wavelengths are particularly useful andare used frequently, these light of these wavelength combinations may besupplied by choosing the appropriate LED chips in each of the foursubsets that emit such combination of wavelengths, even though somewavelengths may be emitted by more than one subset. Thus, each of thefour subsets of LED chips may emit light within a plurality ofwavelength ranges that are different from those of light emitted by atleast one other of the remaining four subsets.

The described embodiments of the present invention produce an intenseand uniformly illuminated area which can be either sent directly intothe microscope or to other optical elements for further beam shaping.FIG. 7A illustrates one embodiment in which a beam expander 7A00 (withoptical components such as lenses 7A01-7A03) is placed in the opticalpath after the collimating/focusing lens 4A06. FIG. 7B illustrates thesame embodiment of the apparatus except that a mirror (item 7B04) isplaced between the collimating lens/focusing lens 4A06 and beam expander7B00 to change the geometry of the light path, which may make packagingmore convenient and compact. Although not shown in any of the figuresexcept for FIG. 4B, the apparatus of the present invention can be fittedwith a variety of mounting adapters, intended to mate mechanically withthe optical ports of multiple brands of microscopes.

FIG. 8 illustrates one embodiment of the present invention using a lightmixing tube as a light scrambler/randomizer, and makes use of a variabledistance between the collector lens and tube entrance as a means ofchanging the effective aperture size. The light mixing tube (item 804),typically constructed of acrylic with many small diffractive particlesembedded, can be used in place of the diffuser and aperture shown inFIGS. 4A and 4B. Similar to a fiber, the separation distance (shown asitem 807) between the collecting lens (item 802) and light mixing tube,determines the accepting angle of the mixing tube and hence acts like avariable aperture that can be adjusted.

Aside from elements such as lenses and light scramblers which canreshape the size or spatial distribution of the light, other opticalelements can be used to modify the spectral distribution of the light aswell. Numerous fluorescence applications benefit from havingexceptionally narrow bandwidths, so narrow band pass filters can be usedto further reduce the spectral distribution of the LED chip(s). FIG. 10illustrates one embodiment of the present invention that uses narrowband pass filters on a filter wheel. Current filter technology canreduce the bandwidth to be less than 1.0 nm. Since the filter does cutoff some optical power, the choice of filters and whether or not to usethem at all will depend on the users' preference between having anarrower bandwidth versus maximally intense light.

The present invention includes a set of LED current driver circuits, andelectronic control, as shown in FIG. 3. The purpose of the LED currentdrivers is to convert the DC voltage provided by the apparatus' AC-to-DCpower supply, to a constant DC current for each of the strings of LEDchips in the LED array. FIG. 9A is a representation of one embodiment ofthe densely packed multiple wavelength LED array used in the presentinvention, with 24 LED chips 9A01 without individual packaging andsupported on a common substrate 9A02, such as a printed circuit board.FIG. 9B shows a cross section of the densely packed multiple wavelengthLED array from FIG. 9A. FIG. 9C is a representation of one configurationof LED array in FIGS. 9A and 9B using 3 LED chips per channel (8channels total). For example, with the LED array configuration of FIG.9C, with eight wavelengths or colors emitted by 8 corresponding groupsor strings of LED chips, configured three chips to a string where the 8groups or strings of 3 LED chips each are labeled “1” to “8” in FIG. 9C,the apparatus would have eight LED current driver circuits, each feedinga constant DC current to one of the colors or wavelengths configuredwithin the LED array. Thus, when used with the LED array configurationshown in FIG. 9C, each LED current driver circuit would be driving astring of three LED chips.

The light emitting area of the LED array in FIG. 9C is of diameter orcross dimension less than 25 mm, and is typically in the range of 8-15mm. By moving the LED array in FIG. 9C along arrows 9C01 and/or 9C02, itis possible to selectively align some of the LED chips with the opticalaxis (not shown) to thereby select the desired wavelengths for thefluorescence microscope. With the above LED chip arrangements, theswapping-in of different wavelength LED “modules” is not needed, nor theuse of dichroic mirrors and other beam-combining optics as in the priorart examples described above.

The electronic control circuitry shown in FIG. 3 performs severalfunctions. The primary function of the electronic control is to turn onand off, as well as control the brightness, of each of the LED colors orwavelengths embodied in the LED array. This is done by directing the LEDcurrent driver circuits to either source a constant DC current, or toturn off the current flow. Brightness control of the LEDs is obtained bychanging the value of the DC current that each LED current drivercircuit provides.

As shown in FIG. 3, user input to the electronic control circuitry ofthe present invention can via a computer interface, or via manual userinterface, or via both interfaces. In one embodiment, the computerinterface is via a USB port. Software that is resident on a user'scomputer will send command messages via the USB interface, to theelectronic control circuitry of the present invention. A microprocessorwithin the electronic control circuitry, running embedded software orfirmware, will interpret the messages sent from the user's computer, inorder to control the states of the illuminator apparatus. The manualuser interface uses a combination of switches, knobs, and a dedicateddisplay, to allow the user to select the color(s) or wavelength(s) ofthe illuminator apparatus, and the brightness of the LEDs, withoutrequiring a separate computer.

Through the use of the USB interface, a separate computer can be used toturn on an off the individual wavelengths of the LED array at a rapidrate, limited only by the speed at which the processor within electroniccontrol circuitry of the present invention is able to process thecommands received over the USB interface. For even faster response, inthe sub-microsecond range, one embodiment of the electronic controlcircuitry has direct digital and analog inputs, that can be used todirectly turn on and off the selected wavelength's LED current drivercircuit, or, alternatively, to directly set the brightness level of theselected wavelength. Switching from one wavelength to another wavelengthis limited by the processing speed of the microprocessor within theelectronic control circuitry. In the case of embodiments of the presentinvention which make use of lateral translation of the position of theLED array, in order to better optimize alignment of the selectedwavelength with the optical axis of the apparatus, then the speed ofswitching between colors may be limited by the time required tolaterally move or position the LED array.

Some fluorescent dyes may have fast decay times. It may be desirable tosynchronize the emission of pulsed light with such decay times bycontrolling the current pulses supplied to the LED chips or strings ofsuch chips. For example, the current pulses may be supplied at afrequency in excess of 100 Hz.

The various embodiments above have the following advantages:

All desired wavelengths or colors are present within a single LED arraysupported by a common substrate, so that the swapping-in of differentwavelength LED “modules” is not needed, nor the use of dichroic mirrorsand other beam-combining optics (as in the prior art examples).

A sophisticated optical design that makes use of the “extended pointsource” nature of the LED array to provide a bright beam of highuniformity across its width, in order to achieve consistent levels offluorescence within the beam. Said optical design consisting of a lightcollecting lens of high numerical aperture, a lightscramble/homogenizer, an aperture, and a focusing/collimating lens ofrelatively large aperture/diameter.

Use of a non-traditional, circular-pattern top-hat diffuser as the lightscrambler/homogenizer element in one embodiment of the presentinvention, to further aid in the achieving of a uniform beam.

Although in many cases the LED array looks sufficiently like a pointsource, to achieve good spatial uniformity of light output, differentembodiments of the present invention allow for lateral translation ofthe array's position, to more optimally align the illuminated portion(wavelength) of the array with the optical axis. (This same idea alsoapplies to the embodiment which uses multiple arrays.)

Use of limited or narrow-bandwidth LEDs, instead of a broadband lightsource (e.g. a metal halide bulb), to waste less of the light output,and also to avoid the use of band-pass filters (either slide-inreplaceable filter elements, or multiple wavelengths of filters on amechanical “filter wheel” or “color wheel”.

Notwithstanding the above claim about avoiding the use of filters, IFthere is an application that demands an even narrower spectrum than whatis provided naturally by the use of LED chips, it IS possible to useadditional filters with the LED illuminator.

The specific optical configuration, including a half-ball lens for lightextraction, a collector lens, a diffusing/scattering/homogenizingelement, an aperture, and a beam focusing/collimating lens.

An additional embodiment that includes a mirror in the optical path tochange the direction of the beam

An embodiment that uses a light guide, optionally with embeddeddiffusing elements, to replace the diffuser and/or aperture of theprimary embodiment. The effective “aperture” of the light guide isdependent on the geometry of the light guide itself, as well as itsposition, or distance from the collecting lens.

The adjustability of the position of both the collecting andfocusing/collimating lenses of the primary embodiment, as a means ofoptimizing the optical performance of the apparatus when used withdifferent brands of microscopes.

The use of electronic control circuitry to enable fast turn on and turnoff of the selected wavelength/color. This includes both the commandsthat can be sent from a remote computer over the USB interface, as wellas a “direct” interface that allows the ON/OFF state of the selectedwavelength/color, and/or its brightness, to be directly controlled viedigital or analog inputs (achieved by bypassing the processor within theelectronic control circuitry, and controlling the selected LED currentdriver directly).

Fast changing between different wavelengths/colors, gated by the speedof the electronic control circuitry, in the embodiments that don'trequire lateral translation or movement of the position of the LEDarray. This is due to the presence of all of the intendedwavelengths/colors within a single LED array (instead of having separatecolors in different LED modules).

While the invention has been described above by reference to variousembodiments, it will be understood that changes and modifications may bemade without departing from the scope of the invention, which is to bedefined only by the appended claims and their equivalents.

We claim:
 1. A LED array spot illuminator for providing light along anoptical axis, comprising: a substrate; at least one array of multipleLED chips without individual packaging supported by said substrate,wherein the LED chips emit light within different wavelength ranges andare distributed laterally with respect to said axis over alight-emitting area, said LED chips having light emitting surfaces foremitting light in directions transverse to said area, an optical elementadjacent to the light emitting surfaces of the LED chips in said atleast one array and in the optical axis collecting light emitted by theLED chips; an optical device that collects and directs light emitted bythe LED chips of the at least one array and collected by said opticalelement along the optical axis; an aperture located in the optical axis,wherein light collected by said optical element and said optical deviceand passed by the aperture forms a beam of light illuminating a spot;and a diffusing/scattering/homogenizing element in the optical axis tohomogenize light within different wavelength ranges so that the beamilluminating the spot is substantially spectrally uniform across thesurface of the illuminated spot.
 2. The illuminator of claim 1, whereinthe diffusing/scattering/homogenizing element is located between the atleast one array of multiple LED chips and the aperture.
 3. Theilluminator of claim 1, wherein the dimensions of the light-emittingarea do not exceed 25 mm.
 4. The illuminator of claim 1, wherein theoptical element and optical device are in the optical axis, saidilluminator further comprising a device for adjusting positions along anoptical axis of the optical element and optical device.
 5. Theilluminator of claim 1, further comprising a device for adjustingpositions along an optical axis of the aperture anddiffusing/scattering/homogenizing element.
 6. The illuminator of claim5, wherein the device adjusts positions along an optical axis of theoptical device, the aperture and diffusing/scattering/homogenizingelement simultaneously.
 7. The illuminator of claim 1, wherein theoptical element comprises a half-ball lens.
 8. The illuminator of claim1, further comprising a mirror or a light guide for directing the lightfrom the optical element to the target.
 9. The illuminator of claim 8,the light guide comprising embedded diffusing elements.
 10. Theilluminator of claim 1, further comprising an electronic control circuitfor supplying electric current to the at least one array of multiple LEDchips, and at least one interface for receiving computer or usercommands for controlling the electric current supplied by the circuit tocontrol light emission by the multiple LED chips.